MATLAB Answers


Detect the hottest spot of a wire in thermal image

Asked by George Anton on 14 May 2018
Latest activity Edited by Image Analyst
on 1 Sep 2018
Hi , i am currently working on a project that i have to detect the hottest spot of the wire in the image i attached.I detected the wire as you see in the second image using the Hough Transform. What i have to do to detect the hottest spot of the wire (as you see an the center of the wire the spot is whiter). I assume that i have to take all the pixels of the wire and compute the average temperature and then compare that temperature again with all the pixels and find where the temperature is higher than the average? On the other hand i don't have the exact temperature of every pixel. Should i find the spot using the color (the whiter the spot the hottest?). And how can i do this?
Thank you


Not sure what your edit just now was, except that you removed your image for some reason.
What about the answer below that I spent so much time making for you? You did not accept it. Why not? Did that solve your problem or not?
Yes it worked! I mistakenly deleted the photos.Thank you very much for your answer.
Could you then please "Accept" the answer by clicking the "Accept this answer" line? Thanks in advance.

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2 Answers

Answer by Image Analyst
on 15 May 2018
 Accepted Answer

Try this:
clc; % Clear the command window.
close all; % Close all figures (except those of imtool.)
clear; % Erase all existing variables. Or clearvars if you want.
workspace; % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
% Have user browse for a file, from a specified "starting folder."
% For convenience in browsing, set a starting folder from which to browse.
startingFolder = pwd
if ~exist(startingFolder, 'dir')
% If that folder doesn't exist, just start in the current folder.
startingFolder = pwd;
% Get the name of the file that the user wants to use.
defaultFileName = fullfile(startingFolder, '*.png');
[baseFileName, folder] = uigetfile(defaultFileName, 'Select a file');
if baseFileName == 0
% User clicked the Cancel button.
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
% The file doesn't exist -- didn't find it there in that folder.
% Check the entire search path (other folders) for the file by stripping off the folder.
fullFileNameOnSearchPath = baseFileName; % No path this time.
if ~exist(fullFileNameOnSearchPath, 'file')
% Still didn't find it. Alert user.
errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
grayImage = imread(fullFileName);
% Get the dimensions of the image.
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
% It's not really gray scale like we expected - it's color.
% Use weighted sum of ALL channels to create a gray scale image.
grayImage = rgb2gray(grayImage);
% ALTERNATE METHOD: Convert it to gray scale by taking only the green channel,
% which in a typical snapshot will be the least noisy channel.
% grayImage = grayImage(:, :, 2); % Take green channel.
% Display the image.
subplot(2, 2, 1);
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo;
axis on;
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0, 0.04, 1, 0.96]);
% Crop the image to get rid of feet and legs.
grayImage = grayImage(1:350, :);
% Filter the image with a top hat filter.
filteredImage = imtophat(grayImage, true(25));
% Display the image.
subplot(2, 2, 2);
imshow(filteredImage, []);
title('Filtered Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Display the image.
subplot(2, 2, 3);
title('Histogram of Filtered Image', 'FontSize', fontSize, 'Interpreter', 'None');
grid on;
% Threshold the image.
% threshold(filteredImage)
binaryImage = filteredImage > 15; % Hgh enough to get rid of bad JPEG artifacts. Never use JPEG for image analysis!
% Display the image.
subplot(2, 2, 4);
imshow(binaryImage, []);
title('Binary Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Extract largest blob only
binaryImage = bwareafilt(binaryImage, 1);
% Display the image.
subplot(2, 2, 4);
imshow(binaryImage, []);
title('Binary Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Find mean intensity
props = regionprops(binaryImage, grayImage, 'MeanIntensity', 'MaxIntensity');
meanIntensity = props.MeanIntensity
MaxIntensity = props.MaxIntensity
% Find hottest spot.
% Get coordinates of pixels in the mask.
[rows, columns] = find(grayImage == MaxIntensity);
% Put a cross at every such intensity on the original image
subplot(2, 2, 1);
hold on;
for k = 1 : length(rows)
xHottestSpot = columns(k);
yHottestSpot = rows(k);
plot(xHottestSpot, yHottestSpot, 'r+', 'MarkerSize', 20, 'LineWidth', 2);
message = sprintf('Number of pixels with max intensity of %f = %d.\n',...
MaxIntensity, length(rows))

  1 Comment

Your code seems to find the line. Can we assume that the line will be straight (unlike the one in the image)? If so, just use imline() to burn that line into a mask (see attached demo). Then use the mask and widen it a bit, say 5 or 9 pixels or whatever. Then use the mask to inspect all the values in the mask:
mask = imdilate(mask, true(9));
meanGrayLevelInMask = mean(grayImage(mask))
maxGrayLevelInMask = max(grayImage(mask))

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Answer by Image Analyst
on 14 May 2018

Use the max function. One way:
maxTemp = max(tempImage(:));
[rows, columns] = find(tempImage == maxTemp);
To find the wire, threshold and call mean.
mask = tempImage > someValue;
meanTemp = mean(tempImage(mask));


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